Fitting in at work: talk to coworkers, but talk less about yourself and spend a lot of time replying to what they have said and relating to it/saying something related to that topic in your life/that you know. Find things in common, the one thing common to you all is where you work and it is easiest to talk about that.
Maybe you're in the wrong job. Do what you love.
You are leaving, At least that should make you feel better, If you have only been there a short time, I am sure it will get better.
Maybe you are at the wrong job. Don't try to fit in with a group of people that you don't feel "right" around. Maybe there is a reason for this.
I always feel better socially if I don't let myself admit to negative feelings, and keep conversation lighthearted with small talk. I guess I think it's good to try to talk about mostly positive things to seem like a happy person. Fake it till you make it.